Spring bolt door locks are the most widely used locks because they provide ease of entry and exit without the use of a key. However, in their locked condition, when a key is required to open the door from the outside of the premises, other methods can be used to overcome the security provided by the lock. These methods include the use of a plastic card, such as a credit card, or a metal shim, which item is inserted into the gap between the strike plate on the door frame and the lock housing mounted on the door and which said item is then brought to bear upon the sloped side of the spring bolt in such a manner that when the plastic card, or metal shim, is pushed further into the door gap the spring of the spring bolt is overcome thus causing the spring bolt to exit from the strike plate cavity and force it back into the lock housing on the door. In this way the door can be readily opened without the use of a key and so the security provided by the lock has been overcome.
A sring bolt and strike plate guard made in accordance with this invention will prevent the spring bolt from being forced out of the strike plate cavity and into the lock housing by any external means, other than the key, and will thus increase the security of the spring bolt to that of a dead bolt, and yet maintain the convenience of the spring bolt lock.
A second method of attack upon the door is kicking or barging the door about a foot above the lock. This action causes the door to bend about the lock bolt which generates a twisting force, or torque, which concentrates the impact on the upper retaining screw of the strike plate. Without the the spring bolt and strike plate guard being installed the applied torque is usually sufficient to cause the upper retaining screw to migrate through the frame closely followed by the lower retaining screw and thus dislodge the strike plate. With the srping bolt and strike plate guard mounted within the bolt cavity the torque force first strikes the xe2x80x98Uxe2x80x99 shaped frame causing it to try to bend within the bolt cavity. This bending motion causes the curved xe2x80x98Uxe2x80x99 arms of the spring bolt and strike plate guard to bear upon its mounting base plate thus redirecting the lateral primary torque, through a 90xc2x0 directional change, into the door frame and cripple and so dissipating the torque force within the door cripple rather than the strike plate, thus maintaining the strike plate integrity.
A spring bolt and strike plate guard made in accordance with this invention will prevent the strike plate from ripping out of the door frame under external impact forces and so will increase the security provided by the strike plate and door lock combination.
The spring bolt and strike plate guard consista of a xe2x80x98Uxe2x80x99 shaped plastic or metal hollow frame cut to such a length that it includes three dimensions. These dimensions being, in the first instance, the depth ofthe bolt cavity cut into the door frame into which the spring bolt and strike plare guard will be mounted. In the second instance, it is that distance between the bolt strike plate mounted on the door frame, above the bolt cavity, and the lock mounting plate on the door edge, this distance being designated as the door gap. And, in the third and final instance, a base plate by which the spring bolt and strike plate guard is mounted within the bolt cavity, this base plate being formed by removing the curved side arms of the xe2x80x98Uxe2x80x99 shaped hollow frame just beyond the distance required in the first two aforesaid instances, such that a flate base, made up of the base of the xe2x80x98Uxe2x80x99 of the xe2x80x98Uxe2x80x99 shaped hollow frame, is formed, which flat base is bent inwards towards the remaining sides of the xe2x80x98Uxe2x80x99 shaped hollow frame to further form a flat base section which is used to mount the spring bolt and strike plate guard to the bottom of the bolt cavity by means of a wood screw inserted through a hole drilled in this flat base section.
Thus, when this spring bolt and strike plate guard, as described above, is placed into the said bolt cavity on the door frame, such that the flat base section bears upon the bottom of the cavity, and the base of the xe2x80x98Uxe2x80x99 shape bears upon the outermost edge of the strike plate aperture, that is the edge closest to the outside of the door, and the curved xe2x80x98Uxe2x80x99 arms bear upon the upper and lower edges of the strike plate aperture, and is then screwed in place by means of the wood screw through the said flat base plate hole, a section of the xe2x80x98Uxe2x80x99 shaped hollow frame will protrude out from the strike plate and into the free space of the door gap. This protruding section envelopes most of the sloping, or cammed, section of the spring bolt, which is the outermost part of the spring bolt, and thus prevents any external body inserted into the door gap reaching the spring bolt.
Since the protruding section of the spring bolt and strike plate guard should fill most of the door gap, and since each door gap may be different, the protruding xe2x80x98Uxe2x80x99 section must be capable of being varied in its length of protrusion. This variation in protrusion length is accomplished by either filing or grinding the protrusion such that it allows free movement of the door.
Further, since the protruding section of the xe2x80x98Uxe2x80x99 shaped hollow frame bears upon the strike plate aperture,any impact force applied to the outside of the door, in an attempt to break the strike plate free of the door frame, and thus allow the door to open, is blocked from acting on the strike plate by the said protrusion absorbing the impact and redirecting the impact force into the door frame and cripple, where it is dissipated.
An object of this invention is the provision of a spring bolt and strike plate guard which will fill the gap between the door frame and the door edge in such a manner that the sloping, or cammed, surface of a spring bolt lock is protected in all dimensions from any external body inserted into the said door gap.
An object of this invention is the provision of a spring bolt and strike plate guard which can be adjusted such that variations in door installations, such as bolt cavity depth and door gap width, can be compensated for.
An object of this invention is the provision of a spring bolt and strike plate guard which will dissipate or deflect, through a 90xc2x0 directional change, any force applied by some external body to the outside of a door, such that the integrity of the strike plate is maintained.
An object of this invention is the provision of a spring bolt and strike plate guard which can be used on any type of door which employs a spring bolt lock.
An object of this invention is the provision of a spring bolt and strike plate guard which is screwed to the bottom of a bolt cavity and thus inhibits tampering with the device.
The above stated and other objects and advantages of the invention will become apparent from the following description when taken with the accompanying drawings and descriptions. It will be understood, however, that the drawings are for purposes of illustration and are not to be construed as defining the scope or limits of the invention, references being had for the latter purpose to the claims appended hereto.